The present invention relates to treatment of nonwoven fabrics to impart desired properties. In particular, the invention provides relatively lightweight nonwoven fabrics with unique properties on opposing surfaces obtained by separate steps in a highly efficient and effective process. The invention also relates to resulting nonwovens having, for example, one surface that is alcohol repellent and the other that has antistatic properties suitable for use in the manufacture of infection control medical products including surgical gowns and sterilization wrap. Such nonwoven fabrics may also have excellent barrier properties as measured by hydrostatic head.
The manufacture of nonwoven fabrics for diverse applications has become a highly developed technology. Well known methods include spunbonding, meltblowing, carding, airlaying, and others. It is not always possible, however, to produce by these methods a nonwoven fabric having all desired attributes for a given application. As a result, it is often necessary to treat nonwoven fabrics by various means to impart such properties. For example, for medical applications such as surgeon""s gowns, barrier to alcohol and blood penetration and bacteria is essential, and antistatic properties are very important. Unfortunately, treatments for barrier properties using fluorocarbons, for example, and treatments for antistatic properties using salts are detrimental to each other which makes it necessary to apply excessive amounts of one or both of the treatments. U.S. Pat. No. 5,178,931 addresses this concern by providing separately treated layers in a multi-ply construction. For lightweight fabrics or single component fabrics this is not always a satisfactory solution to efficiently and effectively providing a two sided nonwoven. European patent 0 546 580 B1 describes a printing process for treating one side only of a hydrophobic nonwoven with a wetting agent resulting in a two sided fabric with hydrophilic and hydrophobic properties. There remains a need, however, particularly for lightweight nonwovens, for improved means and methods for imparting two-sided properties of alcohol repellency and/or antistatic characteristics while maintaining hydrostatic head, all with reduced treatment chemical requirements.
The present invention addresses the difficulties and problems discussed above by providing a two-step treatment process for treating lightweight nonwovens and preserving desired properties of alcohol repellency on one side and/or antistatic characteristics on the other side. The resulting treated nonwoven also has good hydrohead properties. In one embodiment the process involves a saturation treatment for alcohol repellency using a minimum treatment amount followed by a single side spraying of a light amount of antistatic treatment composition. In a second embodiment each side is treated separately with printing forming light spray applications using a minimum of treatment composition resulting in imparting alcohol repellency and/or antistatic characteristics primarily to the respective treated sides only. Other application means are also contemplated. In these preferred embodiments the nonwoven has a basis weight in the range of from about 17 gsm to about 135 gsm and ideally for many applications, in the range of from about 34 to about 88 gsm. The alcohol repellency treatment will generally add only about 0.05 gsm to about 0.41 gsm to the fabric weight and ideally for many applications, within the range of from about 0.10 gsm to about 0.26 gsm. Similarly, the antistatic treatment composition will add only about 0.017 gsm to about 1.08 gsm to the fabric weight and ideally for many applications, within the range of from about 0.068 gsm to about 0.44 gsm. Despite these low add-on amounts, the treated nonwoven will have antistatic properties of less than about 0.50 sec by static decay test (described below) and ideally for many applications less than about 0.05 sec and will also have alcohol repellency of at least 3 to about 70% isopropyl alcohol and ideally for many applications, at least about 3 at 80% isopropyl alcohol. The treated nonwoven will also have a hydrohead of at least about 50 mB and ideally for many applications, at least about 70 mB. The resulting nonwoven is suited for use particularly as infection control products like a medical fabric especially when starting with a spunbond, meltblown or spunbond/meltblown laminate of polymers selected from thermoplastic polymers including polyolefins such as polypropylene, polyethylene as well as copolymers including propylene or ethylene monomer units.